This page walks you through a simple demonstration of how CockroachDB can store and query unstructured JSONB data from a third-party API, as well as how an inverted index can optimize your queries.

Step 1. Install prerequisites

  • Install the latest version of CockroachDB.
  • Install the latest version of Go: brew install go
  • Install the PostgreSQL driver: go get github.com/lib/pq

Step 2. Start a single-node cluster

For the purpose of this tutorial, you need only one CockroachDB node running in insecure mode, so use the cockroach start-single-node command:

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$ cockroach start-single-node \
--insecure \
--store=json-test \
--listen-addr=localhost:26257 \
--http-addr=localhost:8080 \
--background

Step 3. Create a user

Open the built-in SQL shell as the root user and create a new user, maxroach:

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$ cockroach sql --insecure --host=localhost:26257
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> CREATE USER maxroach;

Step 4. Create a database and grant privileges

Next, create a database called jsonb_test:

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> CREATE DATABASE jsonb_test;

Set the database as the default:

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> SET DATABASE = jsonb_test;

Then grant privileges to the maxroach user:

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> GRANT ALL ON DATABASE jsonb_test TO maxroach;

Step 5. Create a table

Still in the SQL shell, create a table called programming:

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> CREATE TABLE programming (
    id UUID DEFAULT uuid_v4()::UUID PRIMARY KEY,
    posts JSONB
  );
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> SHOW CREATE TABLE programming;
  table_name  |                create_statement
+-------------+------------------------------------------------+
  programming | CREATE TABLE programming (
              |     id UUID NOT NULL DEFAULT uuid_v4()::UUID,
              |     posts JSONB NULL,
              |     CONSTRAINT "primary" PRIMARY KEY (id ASC),
              |     FAMILY "primary" (id, posts)
              | )
(1 row)

Step 6. Run the code

Now that you have a database, user, and a table, let's run code to insert rows into the table.

Download the json-sample.go file, or create the file yourself and copy the code into it:

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package main

import (
    "database/sql"
    "fmt"
    "io/ioutil"
    "net/http"
    "time"

    _ "github.com/lib/pq"
)

func main() {
    db, err := sql.Open("postgres", "user=maxroach dbname=jsonb_test sslmode=disable port=26257")
    if err != nil {
        panic(err)
    }

    // The Reddit API wants us to tell it where to start from. The first request
    // we just say "null" to say "from the start", subsequent requests will use
    // the value received from the last call.
    after := "null"

    for i := 0; i < 41; i++ {
        after, err = makeReq(db, after)
        if err != nil {
            panic(err)
        }
        // Reddit limits to 30 requests per minute, so don't do any more than that.
        time.Sleep(2 * time.Second)
    }
}

func makeReq(db *sql.DB, after string) (string, error) {
    // First, make a request to reddit using the appropriate "after" string.
    client := &http.Client{}
    req, err := http.NewRequest("GET", fmt.Sprintf("https://www.reddit.com/r/programming.json?after=%s", after), nil)

    req.Header.Add("User-Agent", `Go`)

    resp, err := client.Do(req)
    if err != nil {
        return "", err
    }

    res, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        return "", err
    }

    // We've gotten back our JSON from reddit, we can use a couple SQL tricks to
    // accomplish multiple things at once.
    // The JSON reddit returns looks like this:
    // {
    //   "data": {
    //     "children": [ ... ]
    //   },
    //   "after": ...
    // }
    // We structure our query so that we extract the `children` field, and then
    // expand that and insert each individual element into the database as a
    // separate row. We then return the "after" field so we know how to make the
    // next request.
    r, err := db.Query(`
        INSERT INTO jsonb_test.programming (posts)
        SELECT json_array_elements($1->'data'->'children')
        RETURNING $1->'data'->'after'`,
        string(res))
    if err != nil {
        return "", err
    }

    // Since we did a RETURNING, we need to grab the result of our query.
    r.Next()
    var newAfter string
    r.Scan(&newAfter)

    return newAfter, nil
}

In a new terminal window, navigate to your sample code file and run it:

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$ go run json-sample.go

The code queries the Reddit API for posts in /r/programming. The Reddit API only returns 25 results per page; however, each page returns an "after" string that tells you how to get the next page. Therefore, the program does the following in a loop:

  1. Makes a request to the API.
  2. Inserts the results into the table and grabs the "after" string.
  3. Uses the new "after" string as the basis for the next request.

Download the json-sample.py file, or create the file yourself and copy the code into it:

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import json
import psycopg2
import requests
import time

conn = psycopg2.connect(database="jsonb_test", user="maxroach", host="localhost", port=26257)
conn.set_session(autocommit=True)
cur = conn.cursor()

# The Reddit API wants us to tell it where to start from. The first request
# we just say "null" to say "from the start"; subsequent requests will use
# the value received from the last call.
url = "https://www.reddit.com/r/programming.json"
after = {"after": "null"}

for n in range(41):
    # First, make a request to reddit using the appropriate "after" string.
    req = requests.get(url, params=after, headers={"User-Agent": "Python"})

    # Decode the JSON and set "after" for the next request.
    resp = req.json()
    after = {"after": str(resp['data']['after'])}

    # Convert the JSON to a string to send to the database.
    data = json.dumps(resp)

    # The JSON reddit returns looks like this:
    # {
    #   "data": {
    #     "children": [ ... ]
    #   },
    #   "after": ...
    # }
    # We structure our query so that we extract the `children` field, and then
    # expand that and insert each individual element into the database as a
    # separate row.
    cur.execute("""INSERT INTO jsonb_test.programming (posts)
            SELECT json_array_elements(%s->'data'->'children')""", (data,))

    # Reddit limits to 30 requests per minute, so don't do any more than that.
    time.sleep(2)

cur.close()
conn.close()

In a new terminal window, navigate to your sample code file and run it:

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$ python json-sample.py

The code queries the Reddit API for posts in /r/programming. The Reddit API only returns 25 results per page; however, each page returns an "after" string that tells you how to get the next page. Therefore, the program does the following in a loop:

  1. Makes a request to the API.
  2. Grabs the "after" string.
  3. Inserts the results into the table.
  4. Uses the new "after" string as the basis for the next request.

The program will loop through that 40 times, but you can start querying the data right away.

Step 7. Query the data

Back in the terminal where the SQL shell is running, verify that rows of data are being inserted into your table:

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> SELECT count(*) FROM programming;
  count
+-------+
    675
(1 row)
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> SELECT count(*) FROM programming;
  count
+-------+
    825
(1 row)

You should see the count increasing. Keep checking until you see 1000 rows.

Now, retrieve all the current entries where the link is pointing to somewhere on GitHub:

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> SELECT id FROM programming \
WHERE posts @> '{"data": {"domain": "github.com"}}';
                   id
+--------------------------------------+
  05348629-d8f1-4c90-99cc-11e8ab313edb
  059a1562-0054-49ff-adc7-aec82c6f74fb
  1b5ea86d-c892-43ba-b40a-c63761aff3ea
  25ac5bfe-44e2-4c6a-892c-959f859ee4e7
  2ab49796-3e55-4a33-8a83-9decef9fbccc
  2df2e3ac-757b-4689-844d-935876df75e9
  4506e0b8-a572-499c-a9c1-2a5075a021f8
  5209ce99-2253-4490-bceb-fd881ff6d962
  56cf90cd-43a9-49e9-a078-3e28c115232f
  57f287a3-d396-460a-a649-9fa41c4315e4
  ...
(90 rows)

Time: 103.748ms
Note:

Since you are querying live data, your results for this and the following steps may vary from the results documented in this tutorial.

Step 8. Create an inverted index to optimize performance

The query in the previous step took 103.748ms. To optimize the performance of queries that filter on the JSONB column, let's create an inverted index on the column:

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> CREATE INVERTED INDEX ON programming(posts);

Step 9. Run the query again

Now that there is an inverted index, the same query will run much faster:

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> SELECT id FROM programming \
WHERE posts @> '{"data": {"domain": "github.com"}}';
(109 rows)

Time: 6.862ms

Instead of 103.748ms, the query now takes 6.862ms.

Step 10. Clean up

If the program is still running, press CTRL + c to terminate it and then use cockroach quit to stop the single-node CockroachDB cluster:

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$ cockroach quit --insecure --host=localhost:26257

If you do not plan to restart the cluster, remove the node's data store:

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$ rm -rf json-test

What's next?

Explore other core CockroachDB benefits and features:

You may also want to learn more about the JSONB data type and inverted indexes.



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